Vehicle air conditioning system with expansion valve control during high pressure cycle conditions

Abstract

A control apparatus for a gas injection type air conditioning system that prevents lowering of compressor speed and cycle stoppage under conditions where high pressure is liable to occur. During a system heating mode, a pressure change rate ASP of the high pressure of the refrigerating cycle is calculated. When a pressure change rate .increment.SP rises above a predetermined value, a system electric expansion valve aperture is reduced. Accordingly, by calculation of the pressure change rate .increment.SP, it is possible to control the electric expansion valve in the above manner earlier than in prior art control schemes when there is a sudden rise in the high pressure.

What is claimed is: 
     
       1. An air conditioning system, comprising: a blower for creating an air current;   an air-conditioning duct that guides air produced by the blower into a compartment;   a compressor having an intake port for taking in low-pressure refrigerant of a refrigerating cycle, a gas injection port for introducing intermediate pressure gas refrigerant of the refrigerating cycle, and a delivery port (22a) for delivering compressed high-pressure refrigerant;   an inside heat exchanger mounted inside the air-conditioning duct for condensing high-pressure refrigerant from the delivery port of the compressor during heating;   first pressure-reducing means for pressure-reducing high-pressure refrigerant from the inside heat exchanger to an intermediate pressure via an electrically-adjustable aperture;   a gas-liquid separator for gas-liquid separating intermediate pressure refrigerant from the first pressure-reducing means;   second pressure-reducing means for pressure-reducing intermediate pressure liquid refrigerant separated in the gas-liquid separator to a low pressure;   an outside heat exchanger for evaporating low-pressure refrigerant from the second pressure-reducing means during heating;   a gas injection passage for guiding intermediate pressure gas refrigerant separated in the gas-liquid separator to the gas injection port of the compressor;   compressor speed controlling means for controlling an operating speed of the compressor; and   controlling means for controlling the aperture of the first pressure-reducing means, for calculating, during heating, a pressure change rate based on information relating to high pressure of the refrigerating cycle, and for reducing the aperture of the first pressure-reducing means when the pressure change rate rises above a first predetermined value.   
     
     
       2. The system of claim 1 wherein the controlling means fixes the aperture of the first pressure-reducing means when the pressure change rate is between the first predetermined value and a smaller second predetermined value. 
     
     
       3. The system of claim 2, wherein the controlling means feedback-controls the aperture of the first pressure-reducing means so that heating capacity of the inside heat exchanger becomes a predetermined capacity when the pressure change rate is less than the second redetermined value, based on information relating to the eating capacity in the inside heat exchanger. 
     
     
       4. The system of claim 3, wherein the controlling means calculates a deviation between a target high-pressure pressure calculated in correspondence with a user-set temperature and a high pressure of the refrigerating cycle, and increases the aperture of the first pressure-reducing means in correspondence with an increase of the deviation using the deviation as information relating to the heating capacity of the inside heat exchanger. 
     
     
       5. The system of claim 1 further comprising compressor load detecting means for detecting a load of the compressor, the aperture of the first pressure-reducing means being reduced when the compressor load detecting means detects that the load exceeds a first predetermined value. 
     
     
       6. The system of claim 5, wherein the compressor decreases in speed when the load exceeds a second predetermined value larger than the first predetermined value. 
     
     
       7. The system of claim 6 wherein the compressor stops when the load exceeds a third predetermined value larger than the second predetermined value. 
     
     
       8. The system of claim 7 wherein the compressor is an electric compressor driven by an electric motor, an inverter for adjusting the speed of the electric compressor, and a current sensor for detecting the current of the inverter, the compressor load detecting means comprising the current sensor. 
     
     
       9. A control apparatus for a motor vehicle air conditioner including an inside heat exchanger operative during a heating mode, a pressure adjustment device to adjust a pressure level of refrigerant passing therethrough, and a compressor having an operating speed dependent on operation of the adjustment device, the apparatus comprising: a control input that receives sensed mode and operating signals;   a control unit that is operative to determine an air conditioner pressure change rate based on the sensed mode and operating signals, and to generate control signals to cause the pressure adjustment device to inhibit an increase in the refrigerant pressure level for a predetermined time period when the pressure change rate is greater than a predetermined value; and   a control output through which the generated control signals are output to the pressure adjustment device to maintain an operating speed of the compressor when the pressure change rate is greater than a predetermined value.   
     
     
       10. The apparatus of claim 9 wherein the controller fixes the pressure adjustment device when the pressure change rate is between the first predetermined value and a smaller second predetermined value. 
     
     
       11. The apparatus of claim 10, wherein the controller controls the pressure reduction device via a feedback loop to adjust the heating capacity of the inside heat exchanger to a predetermined value when the pressure change rate is less than the second predetermined value, based on the sensed operating signals. 
     
     
       12. The apparatus of claim 11, wherein the controller calculates a deviation between a target pressure corresponding to a user-set temperature and a high pressure of the air conditioning circuit and adjusts the pressure reduction device using the deviation as information relating to the heating capacity in an inside heat exchanger. 
     
     
       13. A method of controlling refrigerant pressure in a vehicle air conditioning system during a heating mode, comprising the steps of: determining if a heating capacity deficiency exists based on a calculated heating deficiency value;   detecting if a sudden increase in refrigerant pressure occurs, when a heating capacity deficiency exists, based on a pressure rate of change; and   causing refrigerant pressure to increase in a manner that ensures uninterrupted compressor operation, if a sudden increase is detected.   
     
     
       14. The method of claim 13, wherein the pressure rate of change is determined based on a minimum value of the refrigerant pressure during a predetermined past time period, and a presently detected pressure value. 
     
     
       15. The method of claim 13, wherein the step of causing comprises controlling a system expansion valve to initially suppress an increase in refrigerant pressure to reduce a pressure peak value associated with the increase in refrigerant pressure.